Masson specified a dye he called Ponceau de xylidine for a variant of his trichrome staining method. Although this dye has not been absolutely identified as the dye he used, it is almost certainly the one, and is accepted as such by general consensus. Its use is largely confined to Masson's trichrome, where it gives a slight orange shading to the red of the cytoplasmic structures.
R. D. Lillie.
Conn's Biological Stains
Williams & Wilkins, Baltimore, MD., U.S.A.
Edward Gurr, (1971)
Synthetic dyes in biology, medicine and chemistry
Academic Press, London, England.
Aldrich chemical catalogue, 1992
Aldrich Chemical Company, Milwaukee, WI, USA.